Imprinting is a technique evolved from embossing well known in the field of manufacture of optical disk, which can precisely transfer fine patterns, by pressing a master mold having an irregularity pattern formed thereon (generally referred to as mold, stamper or template) against a resist material to thereby mechanically deform it. In recent years, the imprinting has been expected to be applied to various fields, since a mold, manufactured only once, will be used repetitively and economically for forming fine structures such as nano-structure.
Proposed imprinting processes include thermal imprinting using thermoplastic resin as a material to be processed (see Non-Patent Literature 1, for example), and photo imprinting using curable composition (see Non-Patent Literature 2, for example). In the thermal imprinting, a mold is pressed against a polymer resin heated at or above the glass transition temperature, cooled down to or below the glass transition temperature, and then released to thereby transfer the fine structure onto the resin. The method is very simple and is applicable to a variety of resin materials and glass materials.
On the other hand, in the photo-imprinting, a curable composition is irradiated with light through a translucent mold or light-transmissive substrate for photo-curing, and the mold is then released to transfer the fine pattern onto the photo-cured article. The method enables imprinting at room temperature, and is applicable to the field of high-precision processing such as manufacture of semiconductor integrated circuit. Recent reports have described new developments of nano-casting based on combination of advantages of both processes, and reversal imprinting capable of creating a three-dimensional stacked structure.
Applications below have been proposed for these imprinting processes.
A first application relates to the case where the molded pattern per se has a function, and is usable as an essential component or structural member in nano-technology. Examples include various micro- or nano-optical components, high-density recording media, optical film, and structural members in flat panel display device.
A second application relates to construction of a stacked structure by monolithic molding of micro-structure and nano-structure, or by simple inter-layer alignment, and use of such structure for manufacture of μ-TAS (Micro-Total Analysis System) or biochip.
A third application relates to use of the molded pattern as a mask for processing a substrate typically by etching. With the aid of high-precision alignment and high level of integration, this technique is applicable to manufacture of high-density semiconductor integrated circuit, manufacture of transistor for liquid crystal display device, and processing of magnetic material for next-generation hard disk called patterned medium, replacing the conventional lithographic technique. Efforts for practicing the imprinting, in relation to such applications, have been gathering momentum in these years.
From the beginning, the imprinting has suffered from mold releasability since it involves a process of releasing a mold. As a method of improving the mold releasability, there has been known a method of treating the surface of the mold using a mold releasing agent such as silane coupling agent having a perfluoro group. While the method, capable of reducing the surface energy of mold, is highly effective in terms of improving the mold releasability, the durability has remained insufficient due to degradation of the mold releasing agent as the imprinting is repeated.
As an effort of improving the durability of the mold releasing treatment, there has been known a method of incorporating a silane coupling agent having a perfluoro group into a curable composition (Non-Patent Literature 3). This method has suffered from poor shelf stability due to reactivity of the silane coupling agent, and this has resulted in increased defect of imprinted pattern.
As an effort of improving the mold releasability, there have been known a method of incorporating a surfactant having a perfluoro group into the curable composition (Patent Literature 1), and a method of incorporating a polymerizable compound having an alkyl group which contains two or more fluorine atoms into the curable composition (Patent Literature 2). These methods are successful in terms of ensuring a good shelf stability of the curable composition, which has been degraded by the silane coupling agent.
In recent years, ink jet process has attracted a lot of attention particularly in applications in need of precisely forming ultra-fine patterns (for example, etching resist for processing semiconductor substrate) (Patent Literature 3). The ink jet process, capable of controlling the amount of the curable composition depending on sparseness and denseness of pattern, can successfully reduce variation in the thickness of residual film. The process also takes an advantage over spin coating, in terms of efficiency of utilization of material. Meanwhile, the process has suffered from incomplete filling of the curable composition or non-uniform thickness of the residual film, if ink jetting is inaccurate and unstable.